Today's microprocessors are the powerful descendants of the von Neumann
1 computer dating back to a memo of Burks, Goldstine, and von Neumann of
1946. The so-called von Neumann architecture is characterized by a se-
quential control flow resulting in a sequential instruction stream. A
program counter addresses the next instruction if the preceding
instruction is not a control instruction such as, e. g., jump, branch,
subprogram call or return. An instruction is coded in an instruction
format of fixed or variable length, where the opcode is followed by one
or more operands that can be data, addresses of data, or the address of
an instruction in the case of a control instruction. The opcode defines
the types of operands. Code and data are stored in a common storage that
is linear, addressed in units of memory words (bytes, words, etc. ). The
overwhelming design criterion of the von Neumann computer was the
minimization of hardware and especially of storage. The most simple
implementation of a von Neumann computer is characterized by a microar-
chitecture that defines a closely coupled control and arithmetic logic
unit (ALU), a storage unit, and an I/O unit, all connected by a single
connection unit. The instruction fetch by the control unit alternates
with operand fetches and result stores for the AL U.